This invention relates to combustion chambers in gas turbine engines. In particular, the invention relates to the mounting and alignment of combustion liners within the combustion chambers of gas turbines.
The combustion system of a gas turbine generates hot gases to drive a turbine. The turbine, in turn, drives a compressor that provides compressed air for combustion in the combustion system. In addition, the turbine produces usable output power. A combustion system for a gas turbine may be configured as a circular array of combustion chambers arranged to receive compressed air from the compressor, inject fuel into the compressed air to create a combustion reaction, and generate hot combustion gases for the turbine. Each cylindrical combustion chamber includes one or more fuel nozzles, a combustion zone within the combustion liner, a flow sleeve surrounding and radially spaced from the liner, and a gas transition duct between the combustion chamber and turbine.
The combustion zone is a volume within the combustion liner in which the fuel/air mixture combusts to generate the hot gases. Compressed air flows from the compressor to the combustion zone through an annular gap between the combustion liner and flow sleeve. Air flowing through this gap cools the outer surface of the liner and flows into the combustion zone through holes in the combustion liner. Compressor air flows between the liner and flow sleeve in a first direction, reverses direction as it enters the combustion liner, and flows as a hot gas in an opposite direction out of the liner and combustor, and to the turbine.
The combustion liner operates in a high temperature environment in which a roaring combustion process generates a stream of high-velocity hot gases that flow through the liner and to the turbine. Heat and vibration from the combustion processes, as well as other mechanical loads and stresses from the gas turbine shake, rattle and otherwise vibrate the combustion liner flow sleeve and the other components of the combustion chamber. Accordingly, the combustion liner should be mounted in the flow sleeve to withstand the heat, vibration and loads imposed by the combustion of gases and other forces that act on the combustion chamber.
Liner stops mount the combustion liner concentrically within the combustion flow sleeve. Three liner stops are typically arranged around on the outer surface of the combustion liner, and bridge a gap between the liner and flow sleeve. Each liner stop on the combustion liner mates with a matching liner stop on an inside surface of the flow sleeve. The liner stops align the liner within the flow sleeve, and with respect to the fuel nozzles and other components of the combustion chamber.
Prior liner stops have had difficulty in aligning the combustion liner in the flow sleeve, especially during assembly of the combustion system. During assembly, the combustion liner is inserted into the cylindrical flow sleeve. The liner stops on the combustion liner fit into the matching liner stops in the flow sleeve. Due to the close tolerances in the fit of liner stops, the stops have had to be precisely aligned as the liner is inserted into the flow sleeve. A misalignment between the liner and flow sleeve often resulted in the liner stops not properly fitting together, and required reassembly or resulted in a defective assembly of the liner and sleeve. The requirement for precise alignment of the combustion liner, slows and complicates the assembly process for a combustion system. In addition, the potential for misalignment between the combustion liner and flow sleeve has resulted in a relatively-high number of defects in combustion systems.
The liner stops support the liner during the extreme vibration and heat that result from combustion within the combustion liner. Vibration and thermal deformations due to the combustion process cause the liner, flow sleeve, and other components of the combustor to vibrate and otherwise move with respect to each other. In particular, the combustion liner thermally deforms and vibrates with respect to the flow sleeve and fuel nozzle. Accordingly, the liner stops should maintain the alignment between the liner, sleeve and flow nozzle despite the vibration forces and deformation inherent in a combustion system.
Prior combustion liner stops suffered from excessive wear of their contacting surfaces. The contact surfaces in liner stops are those surfaces of the male and female stops that are in rubbing contact when the liner is in the flow sleeve. The contacting surfaces in the liner stops support the weight of the combustion liner, and transfer vibration and other dynamic forces between the liner and flow sleeve. These contacting surfaces should also withstand the wear that results as these surfaces rub together. As the liner stops rub together, the contacting surfaces wear away and the fit between these surfaces loosens. As the surface fit loosens, the magnitude of vibration between the liner stops increases because there is more space for the liner stops to rattle against each other. During operation of the combustion system, the liner stops may develop a wear cycle of increasing surface wear, which allows for greater vibratory movements between the liner stops, and which in turn causes even more surface wear.
The vibration/wear cycle of the liner stops can continue until the contacting surfaces wear through and the liner stops fail. When liner stops wear through and fail, the wearing surfaces in the combustion chamber may shift away from the liner stops to other surfaces that are not intended to be in rubbing contact. Similarly, unintended contact between surfaces in the combustion chamber may result due to misalignment as the combustion liner is inserted into the flow sleeve. If the wearing surfaces in a combustor shift away from the liner stops, then the surfaces of, for example, the combustion liner and fuel nozzles may come into rubbing contact. The surfaces of the liner and fuel nozzle are not designed or intended to support the combustion liner or to withstand the rubbing wear that occurs during vibration. When the contacting surfaces shift from the liner stops to other combustor chamber components, the cycle of wear and vibration may continue rapidly until the combustor fails, or until a sufficient clearance develops between the new rubbing surfaces to give way and allow the rubbing surfaces to transfer back to the liner stops or other combustor component. Even when the rubbing contact shifts back to the liner stops, wear damage to the liner, nozzles or other combustion components may cause premature failure of the combustion chamber.
Excessive wear between the liner stops, combustion liner and flow sleeves requires frequent maintenance inspections of the liners and stops and can lead to combustor failure. In the past, excessive wear of liner stops has necessitated that gas turbines be regularly shut down to inspect and replace worn combustion components and, in particular, liner stops. These inspections incur high labor costs, require expensive part replacements, and result in lost power generation from the shut-down gas turbines. Accordingly, there is a long-felt need for combustion liner stops that allow for easy alignment of the combustion liner and flow sleeve during assembly, provide vibration resistant support for the sleeve and do not fail due to vibratory wear.